Simplescope

Simplescope is a simple solution for data acquiring, signal visualizing and analysis.
It is build up from three components:

SISAM – PIC-based dual channel sampler
SISAM1 a COM interface to SISAMSISAN – Windows application that controls sampler, acquires and visualizes logical signals
Please follow respective link to read more about components and their capabilities.
To get the best performance you will also need a high speed serial driver, such as Serial XP by Leo Yuriev or HiSerial.

SISAM hadware is cheap and simple enough to be built at your own.
All sofware is free and available for download:Download Simplescope v1.1